This project is studying the enzymatic synthesis of water-insoluble substrates by the liver. Specific examples include the conversion of squalene to cholesterol and the conversion of palmityl-CoA to triacylglycerols. The conversion of squalene to cholesterol requires microsomal membranes and at least two sterol carrier proteins. Sterol carrier protein 1 (SCP1) is required for the conversion of squalene to lanosterol. We are purifying sterol carrier protein2 (SCP2) which is involved in the conversion of lanosterol to cholesterol by rat liver microsomal membranes. The mechanism of action of sterol carrier proteins is under investigation.